Corrosion inhibited paint remover

ABSTRACT

A PAINT REMOVER COMPOSITION COMPRISING A SOLUBLE METASILICATE IN COMBINATION WITH A METAL CORROSION INHIBITOR CONSISTING OF SODIUM AND POTASSIUM STANNATE.

United States Patent Office 3,687,857 Patented Aug. 29, 1972 US. Cl.252109 6 Claims ABSTRACT OF THE DISCLOSURE A paint remover compositioncomprising a soluble metasilicate in combination with a metal corrosioninhibitor consisting of sodium and potassium stannate.

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto us of any royalty thereon.

This invention relates to a composition having utility in the removal ofpaints from metals. More particularly, it relates to the inclusion of asmall amount of sodium or potassium stannate in a metal paint removingcomposition to inhibit the corrosion of aluminum or alloys thereof.

Sodium and potassium chromates are usually utilized in paint removingformulations to inhibit the corrosion of the metal. However, thedisposal of waste chromates constitutes a problem in that solublechromates are poisonous. Accordingly, many municipalities severely limitthe chromium concentration permitted to enter effluent streams orwaterways. The allowable hexavalent chromi um concentration suggested bythe U.S. Public Health Service for the production of fish is 0.50milligram per liter for industrial waste effluent after mixing withreceiving Water. Therefore, it is often necessary to dilute the wastecontaining chromate to a permissible level prior to discharging intoetlluent streams or waterways. When appreciable concentrations ofchromates are needed for proper corrosion inhibition, this becomes alengthy operation.

It is an object of this invention to provide and disclose an effectivecomposition for the removal of paint from a metal.

It is a further object of this invention to provide and disclose acomposition which is non-corrosive to aluminum alloys.

It is a further object of this invention to provide and disclose acomposition comprising an effective corrosion inhibitor which isnon-toxic to wildlife when discharged into efiluent streams orwaterways.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims.

The composition was evaluated for its paint removing ability utilizingtest panels measuring 1" by 3" cut from 28 aluminum sheet (aluminumalloy SAEAAll) having a thickness of 0.034". Sharp edges were removedwith No. 4/0l50 Alundum polishing paper. The aluminum panels wereimmersed for a period of 5 minutes in an 8 ounce per gallon solution oftrisodium phosphate maintained at a temperature of 180 F., water rinsed,immersed in a 50% nitric acid solution for a period of 30 seconds, andagain water rinsed. The panels were then immersed for a period of 5minutes at room temperature in a bath containing one ounce per gallon ofwater of a composition consisting of 20% ammonium bifluoride andchromium trioxide by weight. The panels were then water rinsed, airdried.

The extent of corrosion was determined by weight changes occurring intest panels. Four panels were used in each determination. Test panelsmeasuring /1" by 3" and having a thickness of approximately 0.03 werecut from an aluminum material identical to that utilized in the paintstripping evaluations. The panels were lightly polished with No. 150Alundum paper, washed with acetone, wiped with paper toweling, dippedinto absolute ethyl alcohol and again wiped with paper toweling. Afterweighing to 0.0001 gram, the test panels were immersed in the boilingtest solutions for one hour.

To remove any deposit of inhibitor or corrosion film that had formedduring the test, the panels were immersed in concentrated nitric acid atroom temperature for seconds. The panels were then rinsed under flowingtap water, dipped into absolute ethyl alcohol, dried with papertoweling, weighed to 0.0001 gram and the weight change calculated byditlerence.

The paint removing compositions were evaluated utilizing the paintsystems set forth in Table I below. The paint, which consisted of anolive drab color, was applied by spray to one side of each panel. A coatcomprising a dry film of paint having a thickness of 0.7 to 1.0 mil wasdeposited on the panel.

TABLE I Systems:

(1) One coat alkyd enamel baked for 30 minutes at 300 F., air dried for24 hours, then aged for 24 hours at 120 F.

(2) One coat alkyd enamel modified with 20% ureaformaldehyde, baked for30 minutes at 300 F., air dried for 24 hours, then aged for 24 hours at120 F.

(3) One coat alkyd-red iron oxide-zinc chromate baked for 30 minutes at300 F., cooled to room temperature, and followed by one coat alkydlusterless enamel baked for 30 minutes at 300 F., air dried for 24hours, then aged for 24 hours at 120 F.

(4) One coat alkyd nitrocellulose lacquer dried for 24 hours, then agedfor 24 hours at 120 F.

Illustrative examples of the formulation of the present composition areset forth in Table II below. In said Table II, the sodium metasilicate,sodium and potassium stannate were calculated as anhydrous. Thecommercial sodium and potassium stannate utilized contained fourmolecules of water per molecule of the stannate. A straight or branchedchained dodecylbenzene sodium sulfonate may be utilized.

TABLE II Composition (percent by weight) 1 2 3 4 5 6 7 S 0 11 12 13 1416 Sodium motssilloato 100 08. 77 J8. 77 J8. 35 66.67 57. 14 50.0 66. 6766. 11 00. 11 80. 00 7t]. 21 74. 35 70. 21 73. 53 78. J6 Dodecylbenzenosodium sulionate,

86% active 33. 33 33. 06 33. 06 20. 00 10. 80 18. 50 10. 80 18. 38 10.74 Sodium resinato Sodium hydroxide Sodium stnnnate 1. 23 Potassiumstannate 1. .23 Potassium chromato 1.62 33.33

Composition (percent by weight) 17 18 19 21 22 23 24 26 27 28 20 31 32Sodiummotasilioato 51.14 66.67 66.12 66.12 02.69 62.11 65.04 50.00 80.0070.21 70.21 78.94 75.11 72.11 90.08 Dodecylbenzene sodium suiionatc,

86% active .14.20 33.33 33.06 33.06 31.35 31.06

Sodium resinatc.. Sodium hydroxide Sodium stannatc .82 5.00 Potassiumstannate 6-83 .0.) Potassium chromate 28.57 0 25.00 1.44 6. 22 9. 06

The panels, which were coated in accordance with the rosion inhibition.This is an enormous concentration and paint systems of Table I, werestripped by immersing each would present a major waste disposal problem.panel vertically for a period of one hour in a boiling aque- 20 Example8 illustrates another paint remover formulaous solution of a paintremover consisting of the formulation in which dodecylbenzene sodiumsulfonate is present. tions set forth in Table II, in the concentrationshown in Examples 9 and 10 illustrate complete inhibition attained TableIII, and removing the panels periodically to deterwith a small amount ofsodium or potassium stannate. In mine the extent of paint stripping. Thepanels were then formulation 12 and 14, it is seen that less than oneperevaluated by removing loosened material with a brush 25 cent ofsodium or potassium stannate results in complete under a stream ofrunning water and rinsing with a stream inhibition, although higherpercentages may be utilized as of hot water. The amount of time requiredto remove all shown in formulations 13 and 15. Inefficiency at low conofthe paint was noted. Illustrative examples are set forth centrations ofpotassium chromate is shown by formulain Table III below. tion 16.Formulation 17 discloses that a composition hav- In addition, aqueoussolutions of the formulation of 30 ing a potassium chromate content ofmore than 28% is Table II, in the concentrations shown in Table III,were required to obtain the desired inhibition. Formulation 23 evaluatedin regards to their corrosion properties. Illustraand 24 have the sameproportions of metasilicate and sultive examples are set forth in Table11 below. In said fonate as formulation 18. The low percentage ofchromate Table III, the percent corrosion inhibition has been corinformulation 23 resulted in poor inhibitor properties. rected for ablank, i.e., 0.05 mg. average weight loss. The utilization of a largeramount of chromate in formu- TABLE III Formulation 1 2 a 4 5 6 7 s 9 1011 12 13 14 15 16 Concentration (g./

System:

1 144% 342% 242% 214-215 214-216 2%2% E443; 214-215 2-214 224 22% 24%24% 22% 2-2% 22% 2 5174-6 5544i 531-6 Ski-6 5%6 501 5 ISM-6 5%-6 555-65*?4-6 5 {6 5% 0' 5 545 5%6 5%0 i ti 3 7V 8 'iV -S 7E/-B 7V4; 7 z-S 7%B7%2-3 7V 3 Ty-S 7%43 73 TV S 7} -3 'iV -S 7 -8 0 i4 6-614 043% 66% 66% l-0% 643% 6-015 2?? 2%43 2%3 2%? 272-3 ZVz-3 2 /z-3 2% 3 2 6-3 ones on:

Average wt. loss (mg.) 1.70 .05 .05 1.40 .33 .20 .13 1.58 .05 .05 1.58.05 .10 .05 .00 1.43 Percent inhibition. 0 100 100 18.18 83.03 00.9195.16 0 100 100 0 100 96. 74 100 100 9.80

Formulation 17 18 19 20 21 22 23 24 25 26 27 28 20 30 31 32Concentration (g./

100ml. 3.50 3.00 3.025 3.0% 3.10 3.22 3.033 4.00 2.26 2.285 2.285 2.2932.41 2.51 0.535 2.725 Timelor 100% of coating to be removed (min):

System:

1 2-254 24% 242% 2 2% 2-2% 21 5-3 234-3 2V -3 zyz-s sage 5%4-6 ail-azero me 7-? 2 74% 7-756 14% 06-8 We 716-8 Ms Tie-s 8%0 815-9 892-9 8%-92 5 2 54; m-a zyz-a 2%3 44% 1- 1% 44% +41 Corrosion:

Average wt. loss P(mg)t .10 1.58 .05 .05 .10 .13 1.13 .15 1. 33 .05 .031.05 .85 .15 63.6 .53

erccn inhlbltlor1 96. 74 0 100 100 96. 74 94. 78 29. 41 93.46 0 100 10021. 87 37. 92.19 71. 01

All of the aqueous compositions were effective in the lation 24, i.e.,25%, resulted in improved inhibitor propremoval of paints from thepanels regardless of the corerties. However, it is noted thatformulation 24 is less efrosion inhibitors utilized. Examples 1 to 7 ofTable III fective than formulations 20 and 22 which utilize 0.82%contain 2 grams of sodium metasilicate on an anhydrous sodium andpotassium stannatc, respectively. It is noted basis per 100 ml. of wateron an anhydrous basis, mainthat higher concentrations of the stannatesare not always tained at a pH of 13. It is seen that the weight loss of1.7 as ellectivc as lower concentrations. For example, the mg. offormulation 1, which contains no inhibitor, is utilization of 6.83%potassium stannate in formulation 22 completely eliminated by theutilization of 1.23% of soresulted in 94.78 percent inhibition, whereasthe utilizadium or potassium stannate as shown in Examples 2 and tion of0.82 (formulation 20) resulted in 100% inhibition. 3. Examples 4 through7 show the elTects of using potas- Formulation 25 introduces anotherpaint remover in sium chromate as an inhibitor. It is seen that acomposiwhich sodium resinate is utilized in conjunction with the tionhaving a potassium chromate content of approxisilicate. Formulations 26and 27 show that approximately mately 50% is required in order to obtainthe desired cor- 1% sodium and potassium stannate give completeinhibition. Formulations 28 and 29 show that 1.44% to 6.22% of potassiumchromate are ineffective as inhibitors, but that good corrosioninhibition is obtained with 9.96% chrmate. Formulation 31 illustratesthe fact that the silicate acts jointly with the stannates in producinginhibition. Notwithstanding the maintenance of the solution offormulation 31 at a pH of 12.9, intense attack of the metal results.Formulation 32 illustrates the effect of a pH above 13.0. This solutionis maintained at pH 13.1. Very poor inhibition is obtained withstannates at this pH in boiling solution, indicating a limiting value ofinhibition in the neighborhood of pH 13.0 for boiling aqueous solutions.

Although we have described our invention with a certain degree ofparticularity, we wish it to be understood that we do not desire to belimited to the exact details of formulations shown and described, forobvious modification will occur to a person skilled in the art.

Having described our invention, we claim:

1. A paint removing composition consisting of about 98.77% sodiummetasilicate and about 1.23% alkali metal stannate selected from thegroup consisting of sodium and potassium, said proportions being on apercent by weight basis.

2. An aqueous solution of the composition of claim 1 consisting of about2.025 to 3.220 grams of composition per 100 ml. of solution.

3. A paint removing composition consisting of about 62.11 to 79.21%sodium metasilicate, about 18.38 to 33.08% dodecylbcnzene sodiumsulfonate and about 0.83 to 8.09% alkali metal stannate selected fromthe group consisting of sodium and potassium, said proportions being ona percent by weight basis.

4. An aqueous solution of the composition of claim 3 References CitedUNITED STATES PATENTS 3,034,210 5/1962 De Long 252389 X 2,975,140 3/1961Yaroch 252- 2,947,639 8/1960 Balden ll7l30 X 2,898,246 8/1959 Hannah252-156 X 2,822,325 2/1958 Tinnon et al. 204-54 L X 1,939,421 l2/l933Tosterud 1486.27 X

OTHER REFERENCES The Chemical Formulary, vol. XIII, edited by H.Bennett, 1967, page 195.

Protective Coatings for Metals, by R. M. Burns and W. W. Bradley, 1955,pages 156 and 165.

MAYER WEINBLATT, Primary Examiner D. L. ALBRECHT, Assistant Examiner US.Cl. X.R.

117-l30; l3438; 1486.27; 252l35, 156, 387, 389, 539, DIG 3

